ES2397277T3 - Use of (meth) acrylic polymers in a method for manufacturing an aqueous suspension of calcium carbonate - Google Patents

Abstract

The use, in a method of manufacturing an aqueous suspension of natural calcium carbonate through: a) a grinding stage, b) and possibly a concentration stage in an aqueous medium, of a homopolymer and / or of a copolymer of (meth) acrylic acid characterized in that: - it is carried out during the grinding stage, - it has a molecular weight of between 8,000 g / mol and 15,000 g / mol and preferably between 8,000 g / mol and 12,000 g / mol, - and has a molar content of polymer chains by molecular weight less than 3,000 g / mol of less than 20%, preferably 15%, very preferably 10% as opacity activating agent

Description

Use of (meth) acrylic polymers in a method for manufacturing an aqueous suspension of calcium carbonate

Field of the Invention

Ground natural calcium carbonate or GCC is a mineral pigment commonly used in coatings intended for coating paper sheets, and to provide certain ultimate optical properties such as opacity. Initially, the present calcium carbonate is used in the form of an aqueous suspension, which is simpler to transport, handle and decant than dry powder. Subsequently, said suspension is used in the composition of a paper coating, the latter being used to coat the paper sheet.

A method for the manufacture of said suspension consists in milling said calcium carbonate in water in the presence of a grinding adjuvant, until a determined granulometry is obtained, that is, a determined distribution of particle sizes. During the present stage, an agent known as "grinding adjuvant agent" is used, whose function is to facilitate the mechanical grinding action. Generally, it is a homopolymer or copolymer of acrylic acid, obtained by means of traditional polymerization processes, in emulsion or in solution (see in particular documents FR 2 539 137, FR 2 683 536, FR 2 683 537, FR 2 683 538 , FR 2 683 539, FR 2 683 532 and FR 2 683 533).

WO 02/49766 describes the use of homopolymers and / or copolymers of acrylic acid having a molecular weight between 5,000 and 25,000 in milling processes for manufacturing mineral suspensions in particular calcium carbonate.

United States document 2007/197747 describes the use of homopolymers and / or copolymers of acrylic acid having a molecular weight between 1,000 and 20,000 in calcium carbonate grinding processes.

"Technical information - Targeted Dispersants for Bulk Calcium Carbonate Slurry" Applied Chemical Anwendungs Technik (www.acat.com) describes the use of dispersants in the preparation of calcium carbonate suspensions.

Subsequently, the dry extract of the present suspension (or dry weight amount of calcium carbonate with respect to the total weight of the suspension) is increased by water removal; The purpose of this stage, which has no effect on the granulometry of calcium carbonate, is to provide a final product that is as rich as possible in mineral matter.

Subsequently, it is important to have an aqueous suspension of mineral matter that remains sufficiently fluid over time. This property can be seen very simply by means of BrookfieldTM viscosity measurements of the suspension, immediately after grinding, and then 8 days later, on condition that the medium has not been agitated. This reveals possible inconsistencies related to viscosity, which the person skilled in the art intends to avoid: this constitutes a part of the problem solved by the present invention.

The other restriction, incorporated by means of the present invention, consists in obtaining a calcium carbonate suspension that leads to the highest possible opacity, since this property is desired for the coated paper sheet. And, for a long time, it has been known that opacity is linked to a certain particle size distribution of calcium carbonate within the aqueous suspension. This distribution should be as "next" as possible; Reference is also made to a "vertical" granulometric distribution, with respect to the shape of the graph obtained (percentage by weight of particles having a given diameter as a function of the diameter).

The "verticality" or "proximity" of the particle size distribution is reflected by the "slope factor", f, a parameter well known to those skilled in the art. This slope factor is calculated so that it is equal to the proportion between the percentage by weight of the particles whose diameter is less than a diameter d1 and the percentage by weight of the particles whose diameter is smaller than another diameter d2, that is:

f = (d1 / d2) * 100

The higher the slope factor, "closer" is the distribution of particle sizes, and the better is the opacity of the final coated paper. In particular, this idea is based on the document "Pigment concepts for improved paper and print properties" (P. Burri, ATIP Conference, June 23, 2000 Tour), especially on page 4.

It can also be cited WO 03/089524 which, even though it refers to aqueous kaolin suspensions, indicates a slope factor 100 * (d30 / d70) at least equal to 39, which leads to a paper coated from a coating produced with said kaolin, which has improved optical properties.

Similarly, EP 0 894 836 describes an aqueous suspension of GCC, one of whose characteristics is based on a slope factor (d50 / d20) of between 1.5 and 2, and preferably between 1.5 and 1, 75. Bearing in mind the particular definition provided for the slope factor, the invention is intended for a narrow distribution of particle sizes: it is also indicated that the opacity of the final products is thus improved.

EP 1 579 070 describes a mixture of two carbonate pigments, at least one of which is a GCC having a slope factor of 100 * (d30 / d70) between 30 and 45, preferably between 35 and 45, and very preferably between 37 and 45; the opacity of the coated paper containing these mixtures is subsequently improved (see table 5).

Finally, WO 2007/031870 describes the milling of a precipitated calcium carbonate, or PCC with a GCC, in an aqueous medium, when the co-ground pigment is obtained with a slope factor of 100 * (d30 / d70) of about 30, preferably 40, very preferably 45; subsequently the opacity of the final paper is increased (see table 2).

In parallel to this initial need to grind calcium carbonate to obtain a high slope factor, the person skilled in the art intends to maximize the final dry extract through the second stage of water removal; and this last stage is particularly expensive in terms of energy. Ideally, it would therefore be necessary to grind calcium carbonate to obtain a dry extract in the most favorable way possible, in order to minimize the evaporation stage of water, while maintaining a high slope factor in order to to modify the opacity of the coated paper. Unfortunately, these two requirements are in contradiction with each other.

In fact, the more grinding of calcium carbonate occurs until a highly dry extract is obtained, the more the slope factor deteriorates. This is expressed very clearly in WO 2004/026973 which states (page 2, lines 6-8) that the fact of obtaining a narrow GCC particle size distribution is in opposition to a highly dry extract grinding, since in particular the latter tends to increase the fraction of the finest particles, and thus to a broadening of the particle size distribution. The person skilled in the art who intends on the one hand to minimize the final stage of concentration (i.e., initially grind to the highest possible concentration), while at the same time intending to obtain ultimate properties of improved opacity (by means of a high slope factor not negatively affected by grinding to a concentration that is too high) now faces an unsatisfactory compromise situation.

By continuing your research to offer the expert in the art a solution that allows:

- a higher slope factor than with the prior art grinding adjuvant agents, and therefore get an improved opacity, -At the time it is initially milled at the same concentration, and at the same time eliminating water to it dry final extract, - obtain a final aqueous suspension that is stable over time,

The applicant has developed the use in a method of manufacturing an aqueous suspension of natural calcium carbonate through a grinding stage and a concentration stage in an aqueous medium, of a homopolymer and / or an acid copolymer (met) Acrylic characterized by:

-

It is carried out during the grinding stage,

-

it has a molecular weight between 8,000 g / mol and 15,000 g / mol, and preferably between 8,000 g / mol and 12,000 g / mol,

-

and has a molar content of polymer chains by molecular weight less than 3,000 g / mol of less than 20%, preferably less than 15%, most preferably less than 10%,

as the opacity activating agent.

Throughout the present application, it is indicated that the molecular weights, as well as the polymer chain contents whose molecular weight is less than a certain value, are determined according to a particular method as described in the introduction to the examples.

Similarly, through the term "opacity activating agent", it should be understood an agent that, when used in the method described above, to make an aqueous suspension of calcium carbonate, used by itself to formulate a Paper coating, when it is intended to apply to a sheet of paper, leads to a sheet that has improved opacity. In concrete terms, the person skilled in the art identified a parameter many years ago which, measured in terms of calcium carbonate suspension, varies in the same way as the opacity of the coated paper sheet; This is the light diffusion coefficient of the suspension (S expressed in m2 / kg), in which the latter is applied on a support. In the present application, the inventors rely in particular on the measurement of the present S coefficient in the aqueous suspension of calcium carbonate (the method of measuring the S coefficient is indicated in FR 2 885 906).

Thus, and surprisingly, in comparison with the prior art which is based on the use of a traditional grinding adjuvant agent, that is, a homopolymer and / or a copolymer of (meth) acrylic acid does not satisfy the 2 conditions above, allowing homopolymers and copolymers of (meth) acrylic acid according to the invention:

-

 while grinding with the same dry extract as the prior art, - obtain a higher slope factor 100 * (d25 / d75) and thus a better opacity (S),

-

 while also producing aqueous suspensions that are stable over time.

One of the merits of the applicant is that, satisfactorily, he identified that the choice of a range of specific molecular weights, in combination with a limited fraction of low molecular weight polymer chains, constituted the optimal combination to obtain an aqueous suspension that was on the one hand stable and on the other it presented a high slope factor, which is synonymous with an improved opacity. In addition, it is simple for the person skilled in the art to manufacture polymers having this combination of features, in particular using techniques known as "separation" techniques, and radical controlled polymerization methods such as, in particular, the technique known as technique " RAFT "(reversible addition-fragmentation transfer).

The former are relatively old methods (beginning in the 80s) that are intended to "purify" the polymer as it is obtained after its synthesis. They employ stages that allow populations of polymeric molecular chains that have an insulated molecular weight (through the choice of appropriate solvents and temperatures) and lead, in the first place, to obtaining a given molecular weight, and to the content chosen from polymer chains that have, for example, a molecular weight less than a certain limit. The person skilled in the art may, in particular, refer to United States document 4 507 422.

The second techniques are manufacturing techniques that, in particular through the use of particular catalysts, allow the molecular weight distribution to be controlled during the polymerization reaction. The choice of synthesis conditions (such as, in particular, the ratio of catalyst / monomer used) allows the person skilled in the art to achieve a given molecular weight on the one hand and on the other a content of polymer chains whose molecular weight is lower than a certain limit. In particular, the person skilled in the art can refer to documents WO 02/070571, WO 2004/014967 and WO 2005/095466 (the content of which is included in the reference of the present application, and in particular in relation to claim 4 of the present application) and also to the publications "Dispersion of calcite by poly (sodium acrylate) prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization" (Polymer (2005, 46 (19), 2005, pp 8565-8572) and "Synthesis and Characterization of Poly (acrylic acid) Produced by RAFT Polymerization. Application as a Very Efficient Dispersant of CaCO3, Kaolin and TiO2" (Macromolecules, 36 (9), 2003, pp. 3066-3077).

Furthermore, it is important to underline that none of the aforementioned documents regarding the methods of radical controlled separation and polymerization refers in particular to a method of manufacturing calcium carbonate, by grinding followed by concentration in a medium aqueous. It should be noted herein that this is a particular method, as presented in WO 02/49765, in which an acrylic polymer with very specific neutralization rates in mono- and divalent cations leads to an aqueous suspension. with a reduced amount of grinding adjuvants not adsorbed on the surface of the calcium carbonate. In addition, none of the aforementioned documents relating to radical controlled separation and polymerization techniques provide any information on the ability of a homopolymer or copolymer of (meth) acrylic acid to be a satisfactory opacity activator, if said homopolymer satisfies both particular conditions that constitute the object of the present invention.

Thus, a first objective of the invention is the use, in a method for the manufacture of an aqueous suspension of natural calcium carbonate through:

a) a grinding stage, b) and possibly a concentration step in aqueous medium,

of a homopolymer and / or copolymer of (meth) acrylic acid characterized by:

-

It is carried out during the grinding stage,

-

it has a molecular weight between 8,000 g / mol and 15,000 g / mol, and preferably between 8,000 g / mol and 12,000 g / mol,

-

 it has a molar content of polymer chains by molecular weight less than 3,000 g / mol of less than 20%, preferably 15% and most preferably 10%

as an opacity activating agent.

In a first variant, the present use is also characterized in that said homopolymer and / or copolymer of (meth) acrylic acid is obtained by means of radical polymerization in emulsion or in solution, followed by at least one static or dynamic stage, in which said separation stage employs one or more polar solvents that preferably belong to the group consisting of water, methanol, ethanol, propanol, isopropanol, butane, acetone, tetrahydrofuran or mixtures thereof.

In a second variant, the present use is also characterized in that said homopolymer and / or copolymer of (meth) acrylic acid is obtained by means of radical controlled polymerization, preferably by means of polymerization through reversible addition-fragmentation transfer ( RAFT).

It is important to underline that the person skilled in the art has, using his knowledge and the state of the art, all the elements necessary to manufacture a polymer that verifies the twin characteristics that form the object of the present application; In this sense, it is capable of synthesizing the polymers that form the object of the present invention. In particular, this is emphasized in the state of the art relating to the manufacture of acrylic polymers, in view of controlling both its molecular weight and its poly-molecular index (and thus naturally the amount of oligomers, or the proportion of polymer chains whose molecular weights are less than a certain value). Reference is made to the aforementioned documents (see the top of the previous page).

In this second variant, the present use is also characterized in that the polymerization by means of reversible addition-fragmentation transfer uses at least one chain transfer agent, as claimed in WO 02/070571, WO 2004 / 014967 and WO 2005/095466 (the content of which is included by reference in the present application and in particular in relation to claim 4 of the present application).

In general, the present use is also characterized in that said homopolymer and / or copolymer of (meth) acrylic acid is totally acidic, or totally or partially neutralized by means of a neutralizing agent chosen from sodium and potassium hydroxides, hydroxides of calcium or magnesium and / or oxides, ammonium hydroxide, or mixtures thereof, preferably by means of a neutralizing agent chosen from sodium or potassium hydroxide, ammonium hydroxide, or mixtures thereof, and most preferably by means of a neutralizing agent which is sodium hydroxide.

In general, the present use is characterized in that, in addition to (meth) acrylic acid, said (meth) acrylic acid copolymer contains another monomer chosen from (meth) acrylic anhydride, (meth) acrylamide, (meth) acrylic esters, and preferably between methyl, ethyl, isopropyl, n-propyl, isobutyl, n-butyl, tert-butyl or 2-ethylhexyl acrylates, methyl or ethyl methacrylates, hydroxylate methacrylates, styrene, alpha-methylstyrene, styrene sulfonate, or Acrylamido-2-methyl-2-propane sulfonic acid, ethylene glycol acrylate and methacrylate phosphates, and mixtures thereof, and why this other monomer is preferably acrylamide.

The present use is also characterized in that said homopolymer and / or copolymer of (meth) acrylic acid is used in an amount of 0.1 to 1.0% and preferably 0.2 to 0.6%, in dry weight, with respect to the dry prisoner of calcium carbonate.

The present use is also characterized in that, in addition to said homopolymer and / or copolymer of (meth) acrylic acid, another homopolymer and / or copolymer of (meth) acrylic acid is used together during concentration step b).

The present use is also characterized in that the dry weight concentration of calcium carbonate of the aqueous suspension obtained at the conclusion of step a) is between 35% and 60% of the total weight of said suspension.

The present use is also characterized in that the dry weight concentration of calcium carbonate of the aqueous suspension obtained at the conclusion of the grinding stage b) is between 61% and 78%, preferably between 70% and 75% of the weight total of said suspension.

Examples

Preamble

Throughout the present application, the granulometric characteristics related to calcium carbonate are determined using a SedigraphTM 5100 device, marketed by the MICROMETRICSTM company.

The light diffusion factor S is determined according to the method provided in FR 2 885 906.

Molecular weights and molar contents of polymer chains whose molecular weight is less than a given value are determined using the following method.

A test part of the polymer solution corresponding to 90 mg of dry matter is introduced into a 10 ml flask. The mobile phase is added, with an additional 0.04% DMF, to reach a total mass of 10 g. The composition of the present mobile phase is as follows: NaHCO3: 0.05 mol / l, NaNO3: 0.1 mol / l, triethanolamine: 0.02 mol / l, NaN3: 0.03% by mass.

The CES chain consists of an isocratic pump of the WaterTM 510 type, whose flow rate is set at 0.8 ml / min, a Waters 717+ sample changer, an oven containing a "Guard Column Ultrahydrogel WaterTM" pre-column type , followed by a linear column of the "Ultrahydrogel WatersTM" type, which is 30 cm long and has an internal diameter of 7.8 mm.

Detection is achieved by means of a WatersTM 410 differential refractometer. The oven is heated to a temperature of 60 ° C, and the refractometer is heated to a temperature of 45 ° C.

CES is calibrated with a series of sodium polyacrylate standards supplied by Polymer Standard Service that have a maximum molecular weight between 2,000 and 1 · 106 g / mol and a poly-molecular index between 1.4 and 1.7, and also with a sodium polyacrylate of molecular weight equal to 5,600 g / mol and a poly-molecular index equal to 2.4.

The calibration chart is linear and takes into account the correction obtained using the flow marker (DMF).

The acquisition and processing of the chromatogram are achieved through the use of the 4.02 application of PSS WinGPC Scientific. The chromatogram obtained in the area corresponding to molecular weights greater than 65 g / mol is incorporated.

Example 1

The present example illustrates the use, in a method for the manufacture of calcium carbonate by means of grinding followed by concentration, of a polymer according to the invention or according to the prior art in the course of the grinding stage, in which a given dispersant polymer is used during the concentration step. It illustrates the influence of the polymers used during the grinding stage on the stability of the suspensions obtained at the end of the method (measurement of certain BrookfieldTM viscosities at different times) and also on the distribution of particle sizes - slope factor f = 100 * (d25 / d75) - and on the light diffusion coefficient (S).

For each of the tests nº. 1 to 10, the first stage consists of grinding in water, according to the methods known to those skilled in the art (reference is made to the grinding protocol described in WO 02/49765), a calcium carbonate which is a Carrara marble, of average diameter approximately equal to 10 µm.

The purpose of the present grinding stage is to obtain a dry weight content of calcium carbonate equal to 50% of the total weight of the suspension. It is carried out in the presence of 0.45% dry weight of a polymer according to tests no. 1 to 10, with respect to the total dry weight of calcium carbonate.

In a second stage, the suspension is concentrated (water removal with an EPCONTM manufacturing laboratory thermal evaporator).

The purpose of this second concentration stage is to obtain a dry weight content of calcium carbonate equal to 71% of the total weight of the suspension.

This concentration step is achieved in the presence of 0.25% dry weight with respect to the dry weight of calcium carbonate, of a mixture (70/30 weight ratio) of an acrylic acid homopolymer, of molecular weight equal to

10,400 g / mol, in which 100% of the carboxylic sites in terms of moles are neutralized by sodium hydroxide, and phosphoric acid.

Test No. one

The present test illustrates the prior art and uses an acrylic acid homopolymer (according to WO 02/49765) obtained by means of traditional radical polymerization not followed by separation, whose 50% active sites in terms of moles are neutralized by sodium, 15% by calcium and 15% by magnesium, of molecular weight equal to 9,600 g / mol and whose 25% polymer chains in terms of moles have a molecular weight less than

3,000 g / mol.

Test No. 2

The present test illustrates the prior art and uses an acrylic acid homopolymer obtained by means of traditional radical polymerization not followed by separation, completely neutralized by sodium hydroxide, of molecular weight equal to 3,100 g / mol and whose 65% polymer chains in terms of moles, it has a molecular weight of less than 3,000 g / mol.

Test No. 3

The present test illustrates the prior art and uses an acrylic acid homopolymer obtained by means of traditional radical polymerization not followed by separation, completely neutralized by sodium hydroxide, of molecular weight equal to 5,500 g / mol and whose 37% polymer chains in terms of moles, it has a molecular weight of less than 3,000 g / mol.

Test No. 4

The present test illustrates the prior art and uses an acrylic acid homopolymer obtained by means of traditional radical polymerization not followed by separation, completely neutralized by sodium hydroxide, of molecular weight equal to 5,700 g / mol and whose 40% polymer chains in terms of moles, it has a molecular weight of less than 3,000 g / mol.

Test No. 5

The present test illustrates the prior art and uses an acrylic acid homopolymer obtained by means of RAFT, completely neutralized by sodium hydroxide, of molecular weight equal to 8,150 g / mol and whose 24% polymer chains in terms of moles have a weight molecular less than 3,000 g / mol.

Test No. 6

The present test illustrates the prior art and uses an acrylic acid homopolymer obtained by means of traditional radical polymerization not followed by separation, completely neutralized by sodium hydroxide, of molecular weight equal to 9,400 g / mol and whose 27% chains Polymers in terms of moles have a molecular weight less than 3,000 g / mol.

Test No. 7

The present test illustrates the prior art and uses an homopolymer of acrylic acid obtained by means of traditional radical polymerization not followed by separation, completely neutralized by sodium hydroxide, of molecular weight equal to 33,100 g / mol and of which 17% of chains Polymers in terms of moles have a molecular weight less than 3,000 g / mol.

15 Test No. 8

The present test illustrates the prior art and uses an homopolymer of acrylic acid obtained by means of RAFT, completely neutralized by sodium hydroxide, of molecular weight equal to 31,000 g / mol and whose 12% polymer chains in terms of moles have a weight molecular less than 3,000 g / mol.

Test No. 9

The present test illustrates the invention and uses an acrylic acid homopolymer obtained by means of traditional radical polymerization followed by separation, completely neutralized by sodium hydroxide, of equal molecular weight.

25 to 11,500 g / mol and whose 17% polymer chains in terms of moles have a molecular weight less than 3,000 g / mol.

Test No. 10

The present test illustrates the invention and uses an homopolymer of acrylic acid obtained by means of RAFT, completely neutralized by sodium hydroxide, of molecular weight equal to 10,800 g / mol and whose 18% polymer chains in terms of moles have a weight molecular less than 3,000 g / mol.

Test No. eleven

The present test illustrates the invention and uses a homopolymer of acrylic acid / methacrylic acid (90/10 in terms of% by weight) obtained by means of traditional radical polymerization followed by separation, completely neutralized by sodium hydroxide, of molecular weight equal to 11,000 g / mol and whose 16% polymer chains in terms of moles have a molecular weight less than 3,000 g / mol.

Test No. 12

The present test illustrates the invention and uses a homopolymer of acrylic acid / methacrylic acid (90/10 in terms of% by weight) obtained by means of a RAFT method, completely neutralized by sodium hydroxide, of molecular weight equal to 9,000 g / mol and whose 16 mol% polymer chains have a molecular weight less than

3,000 g / mol.

Table 1 shows the characteristics of the polymers used during the grinding stage. The values of the dry extracts are also provided after the grinding stage a) and the concentration stage b) (referred to

50 respectively as ESa and ESb), together with the percentages by weight of the particles whose diameters are smaller than 1 µm and 2 µm (referred to respectively as% <1 µm and 5 <2 µm).

Test No.

one 2 3 4 5

Prior art / Invention ("IN")

PA PA PA PA PA

Mw (g / mol)

9,600 3,100 5,500 5,700 8,150

% <3,000 g / mol

25 65 37 40 24

That (%)

49.6 51.7 49.8 fifty fifty

It is B (%)

71.3 71.2 71.0 71.1 71.0

% <1! M

73.2 73.7 74.9 73.9 73.2

% <2! M

96.2 95.6 93.3 96.0 96.0

Test No.

6 7 8 9 10

Prior art / Invention ("IN")

PA PA PA IN IN

Mw (g / mol)

9,400 33,100 31,000 11,500 10,800

% <3,000 g / mol

27 17 12 17 18

That (%)

fifty - - 50.5 51.4

It is B (%)

71.4 - - 71.0 71.0

% <1! M

73.7 - - 73.4 73.2

% <2! M

95.8 - - 96.3 96.1

Test No.

eleven 12

Prior art / Invention ("IN")

IN IN

Mw (g / mol)

11,000 9,000

% <3,000 g / mol

16 16

That (%)

51.0 51.1

It is B (%)

71.0 71.0

% <1! M

73.2 73.2

% <2! M

96.1 96.0

Table 1

The measurements could not be carried out for tests Nº. 7 and 8, since grinding was not possible. These polymers, which have a too high molecular weight, do not allow calcium carbonate to be ground until a dry extract close to 50% is reached.

10 In a second stage, for tests Nº. 1 to 6, and 9 to 12, the stability of the suspensions obtained was determined, measuring their BrookfieldTM viscosities at times t = 0 and t = 8 days (without prior agitation, at 25 ° C and at 10 revolutions / minute), and they are appreciated respectively as! oy! 8 (mPa · s). Results are shown in table 2.

Test No.

one 2 3 4 5

Prior art / Invention ("IN")

PA PA PA PA PA

Mw (g / mol)

9,600 3,100 5,500 5,700 8,150

% <3,000 g / mol

25 65 37 40 24

! o (mPa · s)

490 6,300 240 250 420

! 8 (mPa · s)

7,000 21,100 2,700 4,700 5,400

Test No.

6 9 10 eleven 12

Prior art / Invention ("IN")

PA IN IN IN IN

Mw (g / mol)

9,400 11,500 10,800 11,000 9,000

% <3,000 g / mol

27 17 18 16 16

! o (mPa · s)

300 560 350 550 650

! 8 (mPa · s)

9,300 2,400 3,100 3,200 3,200

Table 2

20 It is observed that the viscosities obtained for tests Nº. 1, 2, 5 and 6 are greater than 5,000 mPa · s after 8 days; It follows that the corresponding aqueous suspension is difficult to handle and in particular difficult to pump. Such tests are not satisfactory to those skilled in the art.

In a third final stage, in the case of suspensions in which grinding could be achieved, and for

25 which BrookfieldTM viscosities (at 25 ° C at 10 revolutions / minute, 8 days before stirring) were less than 5,000 mPa · s, its slope factor f = 100 * (d25 / d75) was determined, together with its S diffusion coefficient of light. These results are shown in Table 3.

Test No.

3 4 9 10 eleven 12

Prior art / Invention ("IN")

PA PA IN IN IN IN

Mw (g / mol)

5,500 5,700 11,500 10,800 11,000 9,000

% <3,000 g / mol

37 40 17 18 16 16

d25 / d75 * 100

31.0 30.4 32.3 34.0 32.0 32.0

S (m2 / kg)

136 138 141 144 140 140

30 Table 3

Table 3 clearly demonstrates that only trials No. 9 to 12 corresponding to the invention lead to a marked improvement in the slope factor and thus opacity.

As a summary, only homopolymers and copolymers of acrylic acid obtained by means of RAFT or by separation techniques, and which have the dual characteristic of having a molecular weight between 8,000 g / mol and 15,000 g / mol, per one part, and having a molar content of polymer chains having a molecular weight less than 3,000 g / mol of less than 20%, allow:

- grind calcium carbonate under the conditions of the example, -with a view to obtaining suspensions whose rheological properties after 8 days are in accordance with the requirements of the person skilled in the art,

-and whose slope factor and light diffusion coefficient S have been improved.

Claims (8)

1. The use, in a method of manufacturing an aqueous suspension of natural calcium carbonate through: 5 a) a grinding stage, b) and possibly a concentration step in an aqueous medium, of a homopolymer and / or a copolymer of (meth) acrylic acid characterized in that: 10 - is carried out during the grinding stage,

-

it has a molecular weight between 8,000 g / mol and 15,000 g / mol and preferably between 8,000 g / mol and 12,000 g / mol,

-

and has a molar content of polymer chains by molecular weight less than 3,000 g / mol of less than 20%, preferably 15%, very preferably 10%

15 as opacity activating agent. 2. The use according to claim 1, characterized in that said homopolymer and / or copolymer of (meth) acrylic acid is obtained by radical polymerization in emulsion or in solution, followed by at least one static or dynamic stage, wherein said separation stage uses one or more polar solvents that They preferably belong to the group consisting of water, methanol, ethanol, propanol, isopropanol, butane, acetone, tetrahydrofuran or mixtures thereof. 3. The use according to claim 1, characterized in that said acid homopolymer and / or copolymer (meth) acrylic is obtained by means of radical controlled polymerization, preferably by means of polymerization by means of reversible addition-fragmentation transfer (RAFT). 4. The use according to one of claims 1 to 3, characterized in that said homopolymer and / or copolymer of (meth) acrylic acid is totally acidic, or is totally or partially neutralized by a neutralizing agent chosen from hydroxides of sodium or potassium, calcium or magnesium hydroxides and / or oxides, hydroxide of 30 ammonium, or mixtures thereof, preferably by means of a neutralizing agent chosen from sodium or potassium hydroxide, ammonium hydroxide, or mixtures thereof, and most preferably by means of a neutralizing agent that is sodium hydroxide. 5. The use according to one of claims 1 to 4, characterized in that, in addition to (meth) acrylic acid, Said (meth) acrylic acid copolymer contains another monomer chosen from (meth) acrylic anhydride, (meth) acrylamide, (meth) acrylic esters, and preferably between methyl, ethyl, isopropyl, n-propyl, isobutyl, n- acrylates. butyl, tert-butyl or 2-ethylhexyl, methyl or ethyl methacrylates, hydroxylate methacrylates, styrene, alpha-methylstyrene, styrene sulfonate, or acrylamido-2-methyl-2-propane sulfonic acid, acrylate and ethylene glycol phosphate, and their mixtures, and why this other monomer is preferably acrylamide. 6. The use of one of claims 1 to 5, characterized in that said homopolymer and / or copolymer of (meth) acrylic acid is used in an amount of 0.1 to 1.0% and preferably 0.2 to 0 , 6% by dry weight, with respect to the dry weight of calcium carbonate. The use of any one of claims 1 to 6, characterized in that, in addition to said homopolymer and / or copolymer of (meth) acrylic acid, another homopolymer and / or copolymer of (meth) acrylic acid is used jointly during the concentration stage b). 8. The use of any one of claims 1 to 7, characterized in that the dry weight concentration of The calcium carbonate of the aqueous suspension obtained at the conclusion of the milling stage a) is between 35% and 60% of the total weight of said suspension. 9. The use of any one of claims 1 to 8, characterized in that the carbonate weight concentration Calcium of the aqueous suspension obtained at the conclusion of the concentration step b) is between 61% and 55%, preferably between 70% and 75% of the total weight of said suspension.